//@原文链接：https://blog.csdn.net/ITSOK_123/article/details/123982897

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        ListNode* cur = head;
        ListNode* pre = new ListNode();
        ListNode* temp;
        while(cur!=nullptr){
            temp = cur->next;
            cur->next = pre->next;
            pre->next = cur;
            cur = temp;
        }
        cur = pre->next;
        delete(pre);
        return cur; 
    }
};


//迭代法
class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        ListNode* prev = nullptr;
        ListNode* curr = head;
        while (curr) {
            ListNode* next = curr->next;
            curr->next = prev;
            prev = curr;
            curr = next;
        }
        return prev;
    }
};

//递归解法
class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        if(head == NULL || head->next == NULL){
            return head;
        }
        ListNode* nex = reverseList(head->next);
        head->next->next = head;
        head->next = NULL; 
        return nex;
    }
};
